Experimental simulation of the radiation damage using He+ implantation has been performed in research of Fe-Cr model al-loys. Different chromium content in the studied materials enables investigations of the effect of this element on the microstruc-ture of radiation treated materials. The damaged region was investigated with the positron lifetime techniques with focus on the size and distribution of the defects. Our measurements show that not only pulsed low energy positron beam spectroscopy (PLEPS) but also conventional lifetime spectroscopy can study the behaviour of vacancy type defects induced by implantation of charged particles. Our results show that initial microstructure of low Cr alloys with significant presence of vacancy type de-fects is less resistant to creation of defect agglomeration in comparison with higher Cr alloys.